1. Field of the Invention
The present invention relates to an image blur correction unit, a lens barrel device, and a camera apparatus each correcting an image blur caused by a vibration upon image capture, or imaging.
2. Description of the Related Art
Compact cameras are being requested to be further miniaturized and have higher power (magnification) and higher pixel resolution. Accordingly, this leads to an increased frequency of capturing an image blurred due to camera shake upon capturing an image of a subject. As for a mechanism for shifting an optical element to compensate for camera shake, a retractable optical system and an optical-axis bending optical system each include a mechanism axially sliding in two directions. For example, in a related-art mechanism, the center of gravity of an optical element is placed within an area surrounded by four guide shafts axially sliding in two directions.
For example, in an image blur correction mechanism included in a device disclosed in Japanese Patent No. 2720955 (U.S. Pat. No. 5,266,988), a lens holding frame which holds a correction lens is held by a first holding frame having a pair of pitch shafts such that the lens holding frame is movable in the pitch direction. The first holding frame is supported by a second holding frame having a pair of yaw shafts such that the first holding frame is movable in the yaw direction. The correction lens held by the lens holding frame is located in an area surrounded by the pair of pitch shafts and the pair of yaw shafts. Actuators moving in the pitch direction and actuators moving in the yaw direction are each configured such that magnets and a yoke form a magnetic circuit and a coil is placed in the magnetic circuit. Those actuators generate propulsive forces in the pitch direction and the yaw direction, respectively, using magnetic fields generated by currents flowing through the coils.
In the above-described mechanism disclosed in Japanese Patent No. 2720955, the actuators for driving the correction lens in the pitch direction and the other actuators for driving the correction lens in the yaw direction each have to include the magnets and the yoke. In addition, those actuators are arranged so as to surround the correction lens. Accordingly, the size of the image blur correction mechanism is increased in the direction orthogonal to the optical axis of the correction lens, thus upsizing a lens barrel and the whole of a camera and increasing the number of components. This leads to an increased cost.
In an optical-axis bending lens system in which the optical axis is bent at an angle of 90 degrees, if a correction lens is placed in an area surrounded by four shafts in a manner similar to Japanese Patent No. 2720955, it is difficult to reduce the thickness of a lens barrel, namely, further reduce the thickness thereof in the direction along the optical axis.
Assuming that the correction lens is placed in the area surrounded by the four shafts, in order to reduce the size or thickness of the mechanism, an opening of a holding frame has to be sufficiently larger than the optical effective aperture. Upon reducing the size or thickness of the mechanism, however, it is difficult to ensure that the opening is sufficiently larger than the optical effective aperture. Disadvantageously, a stray light component may enter the optical path, thus causing a ghost image.
The mechanism, in which the correction lens is placed in the area surrounded by the four shafts, functions as an image blur correction unit. The correction unit is incorporated as one unit into a lens barrel. Since this unit is incorporated in the lens barrel, the unit is affected by the size of a frame of the lens barrel. In the unit including a pair of pitch shafts and a pair of yaw shafts, a movable range of the correction lens held by the lens holding frame is also affected by the thickness of the frame constituting the body of the lens barrel. Accordingly, the movable range of the correction lens is restricted by the thickness of the frame. Even when an enough movable range is provided, it is difficult to reduce the size of the image blur correction unit.
As for the pair of pitch shafts and the pair of yaw shafts in this unit, both ends of each shaft are secured to the lens holding frame. A hole in each boss provided for the lens holding frame serves as a slide hole along which the lens is slidable in the axial direction of the corresponding shaft. The accuracy of the sliding direction of the correction lens is determined by the accuracy of the axial direction of each shaft and that of the axial direction of the slide hole in the corresponding boss. Accordingly, so long as the accuracy of the slide hole is not high, it is difficult to correct an image blur with high accuracy.